Abstract

Plasmaoxidation of the c-Si substrate through a very thin gate oxide layer can be observed during based plasma overetch steps of gate etch processes. This phenomenon generates the so-called silicon recess in the channel and source/drain regions of the transistors. In this work, the authors compare the silicon recess generated by continuous wave plasmas and synchronous pulsed plasmas. Thin layers are exposed to continuous and pulsed plasmas, reproducing the overetch process conditions of a typical gate etch process. Using in situellipsometry and angle resolved X-ray photoelectron spectroscopy, the authors demonstrate that the oxidized layer which leads to silicon recess can be reduced from 4 to 0.8 nm by pulsing the plasma in synchronous mode.